The present invention relates to a vehicle method and system for controlling stiffness of at least one support structure of a vehicle during acceleration, braking and cornering and absorbing energy in a vehicle collision.
The dynamic behavior of flexible beams, plates and shells is important to the effective operation of many structures, such as automobiles, aircrafts and space platforms. With appropriate control, fatigue failure can be avoided and undesirable resonance can be eliminated. One known arrangement shown in prior art FIG. 1 is a beam structure 10 that includes a magnetorheological (MR) layer 12 surrounded by aluminum layers 14, 16. The MR layer 12 is sealed within and between the aluminum layers 14, 16. The aluminum layers 14, 16 can be considered a pair of plates and the MR layer 12 is a magnetorheological fluid in one known structure. This structure is set forth in “An adaptive beam model and dynamic characteristics of magnetorheological materials” Sun et al., Journal of Sound and Vibration 261 (2003) pp. 465-481. The MR layer 12 is in liquid form when there is no external stimuli. Applying a magnetic field to the beam or support structure 10 shown in FIG. 1 changes the MR layer to become more like a solid gel. Thus, the resonant frequency of the beam structure 10 that results in vibration of the beam structure can be changed by the magnetic field to avoid undesirable vibration that may result in noise. Further, fatigue failure for a beam structure 10 can be avoided by eliminating resonant vibration. In response to the magnetic field, the gel or MR layer 12 becomes more solid, resulting in an increased stiffness and decreased flexibility or pliability for the beam structure 10. Therefore, changing properties of the beam structure 10 occurs in response to the magnetic field.
Other structures are made from known magnetorheologic elastomers (MREs). These elastomers include one or more of soft magnetic particles, hard magnetic particles, magnetostrictive particles and magnetic shape-memory particles. Solid and porous matrix structures are known.
Known electrorheological (ER) materials or layers have also been embedded or otherwise disposed, for instance, in a laminated composite for controlling vibration thereof in a similar manner by applying electricity thereto. The electrorheological (ER) materials or the MR layer disposed in a composite, can be in the shape of beams, plates and shells.
Other known materials change properties in response to external stimuli. One known arrangement is a meta-material that includes a deformable structure coupled to a rigid element. Thus, at least two materials are required. In operation, when activated by electrostatic coupling, the meta-material increases in stiffness, damping or other mechanical properties. In one known structure, electrodes provide electrical current to increase stiffness. Other materials that change properties are provided in a group consisting of a piezo ceramic, a piezo polymer, an electrorestrictive ceramic, a polymer gel, a shape-memory alloy, and a shape-memory polymer. These known materials are disclosed in U.S. Pat. Pub. 2006/0192465.